What does this light mean on the dashboard?

Has that red icon of a car just appeared or has it always been there? I think it tells you at a quick glad that all your doors are completely shut. Open a door and look see if the image changes. I've hauled stupid people who open the door, get out, walk away, and leave the door wide open. They even ignore me when I tell them to shut the door. Now, how stupid is that? I should buy a Lexus next time, or quit hauling stupid people.